Method for producing nickel powder

ABSTRACT

Provided is a production method for maintaining the quality while keeping a high operating rate of the reaction by continuously feeding a solution, seed crystals, and hydrogen gas into a reactor to produce nickel powder, and continuously discharging the resulting powder. The method for producing nickel powder comprises feeding a nickel ammine sulfate complex solution and seed crystals into a reactor, and feeding hydrogen gas into the reactor to subject a nickel complex ion in the nickel ammine sulfate complex solution to a reduction treatment and to thereby produce nickel powder, wherein, in the reduction treatment, while the nickel ammine sulfate complex solution is being continuously fed into the reactor, a temperature inside the reactor is controlled within the range of 150 to 185° C. and the feed rate of hydrogen gas is controlled to maintain an inner pressure of the reactor in the range of 2.5 to 3.5 MPa.

BACKGROUND Field of the Invention

The present invention relates to a method for obtaining nickel powderfrom a nickel ammine sulfate complex solution, and specifically relatesto a method for continuously adding a solution and hydrogen gas etc., toa high pressure container, and continuously discharging and recoveringnickel powder.

Related Art

As a method for industrially producing nickel powder using ahydrometallurgical process, a method for producing nickel powderdisclosed in Japanese Patent Application Laid-Open No. 2015-140480 isknown, in which a raw material containing nickel is dissolved in asolution of sulfuric acid, followed by liquid-purification step ofremoving impurities contained in the dissolution, and thereafter ammoniais added to the resulting nickel sulfate solution to form a nickelammine complex; and the nickel ammine sulfate complex solution is thenplaced into a container at high temperature and high pressure, andhydrogen gas is fed to reduce nickel in the nickel ammine sulfatecomplex solution.

Because the reaction is performed at high temperature and high pressurein such a production method as described above, batch methods forproduction are often used from the viewpoint of ease of handling andcost of the apparatus. However, in such batch methods for production, aseries of operation to open the reactor, place the solution, tightlyseal the reactor, heat the reactor, control the temperature and thepressure, blow hydrogen gas into the reactor to perform reduction, coolthe reactor, and extract the reaction product should be performed ateach stage. For this reason, the batch methods are not efficient becausethe methods require large amounts of labor and time, reducing theoperating rate. Furthermore, influences of heating and/or cooling beforeand after the reaction cannot be neglected, causing uneven precipitatescalled scaling or a variation in particle size during the reaction insome cases. In particular, uneven nickel powder produced due to mixingof coarse nickel powder is more likely to cause wear or clog of thefacility during handling, reducing the operating rate. The influences ofuneven nickel powder as well as the labor to remove it result indifficulties in maintaining the operating rate of the reaction and thequality of products at constant levels.

Nickel powder obtained by the batch method has a problem about thequality of impurities compared to the electrolytic nickel in the form ofa plate (sheet) obtained by standard electrometallurgy. Specifically,the sulfur grade should be 0.01% by weight or less to obtain thecertification of high purity grade in an international nickel marketLondon Metal Exchange (LME). The nickel powder obtained by the batchmethod may have higher sulfur grade than that in the high purity nickelof the LME grade specified in the LME, and are difficult to use inapplications where the electrolytic nickel is completely replaced.

An object of the present invention provides a method for continuouslyfeeding a solution, seed crystals, and hydrogen gas into a reactor keptat high temperature and high pressure to produce nickel powder, andcontinuously discharging and recovering the produced powder, whereby afine nickel powder with high purity can be sufficiently grown, avariation in particle size can be reduced to maintain the quality of thenickel powder, and a high operating rate of the reaction can bemaintained.

SUMMARY

A first aspect of the invention relates to a method of producing nickelpowder, where the method includes the steps of feeding a nickel amminesulfate complex solution and seed crystals into a reactor, and feedinghydrogen gas into the reactor to subject a nickel complex ion in thenickel ammine sulfate complex solution to a reduction treatment and tothereby produce nickel powder having a sulfur grade of lower than 0.01%by weight, wherein, in the reduction treatment, while the nickel amminesulfate complex solution containing polyacrylic acid in a concentrationof 0.5 to 1.0 g/liter is being continuously fed into the reactor, atemperature inside the reactor is controlled within the range of 150° C.or more and 185° C. or less and the feed rate of hydrogen gas iscontrolled to maintain an inner pressure of the reactor in the range of2.5 to 3.5 MPa to produce a nickel powder slurry containing the nickelpowder, and thereafter, when the nickel powder slurry is extracted fromthe reactor, a feed amount of the nickel ammine sulfate complex solutionand the seed crystals and a discharge amount of the nickel powder slurryare adjusted to keep a given amount of the solution in the reactor.

A second aspect of the present invention relates to a method ofproducing nickel powder, where the method includes the steps of feedinghydrogen gas into a reactor, and feeding a nickel ammine sulfate complexsolution and seed crystals into the reactor to subject a nickel complexion in the nickel ammine sulfate complex solution to a reductiontreatment and to thereby produce nickel powder having a sulfur grade oflower than 0.01% by weight, wherein, in the reduction treatment, thenickel complex ion in the nickel ammine sulfate complex solution isreduced in such a manner that a slurry containing ammonium sulfate andnickel powder are stored in the reactor to form a liquid phase portionand a gaseous phase portion in the reactor and an inner pressure of thegaseous phase portion is controlled through the feeding of the hydrogengas into the reactor, a slurry containing seed crystals and the nickelammine sulfate complex solution containing polyacrylic acid in aconcentration of 0.5 to 1.0 g/liter are continuously fed into the liquidphase portion, a temperature inside the reactor is controlled in therange of 150° C. or more and 185° C. or less, and the feed rate of thehydrogen gas is controlled to maintain an inner pressure of the reactorin the range of 2.5 to 3.5 MPa, to produce a nickel powder slurrycontaining the nickel powder, and thereafter, when the nickel powderslurry is extracted from the reactor, a feed amount of the nickel amminesulfate complex solution and the seed crystals and a discharge amount ofthe nickel powder slurry are adjusted to keep a given amount of thesolution in the reactor.

Nickel powder having an average particle size in the range of 0.1 to 100μm may be used as the seed crystals according to the first aspect of theinvention or the second aspect of the invention.

Nickel powder having an average particle size in the range of 0.1 to 10μm may be used as the seed crystals according to the first aspect of theinvention or the second aspect of the invention.

The amount of the seed crystals to be added according to theabove-described aspects may be in the range of 1 to 100% by weight basedon the weight of nickel contained in the nickel ammine sulfate complexsolution.

The nickel ammine sulfate complex solution that is subjected to thereduction treatment may contain polyacrylic acid in an amount in therange of 0.5 to 5% by weight based on the weight of the seed crystals inthe nickel ammine sulfate complex solution.

The reduction treatment according to the invention may includecontinuously feeding into the reactor the nickel ammine sulfate complexsolution containing the seed crystals such that the reaction time of thereduction treatment in the reactor takes 5 minutes or more and 120minutes or less.

According to the present invention, a nickel precipitate can be formedon seed crystals and a grown nickel powder can be formed thereon throughthe repeated reduction treatment with the precipitation of nickel. Inaddition, nickel powder having a little variation in size can becontinuously obtained.

Also, because of the effect of the dispersant, the nickel powder havinglower sulfur grade can be extracted and recovered from the solution inthe form of fine powdery precipitate. Furthermore, a coarse nickelpowder having a spherical shape and a smooth surface can also beobtained depending on the combination of the particle size of the nickelpowder and the concentration of the dispersant.

The nickel powder produced in the present invention can be used inapplications of nickel pastes as an inner constitutional substance ofstacked ceramic capacitors. This production method can grow particlesthrough repetition of the reduction treatment with hydrogen to obtain ahigh purity nickel metal of high quality while maintaining a highoperating rate of the reaction. This method attains an industriallyremarkable effect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 This illustrates an optical microscope photograph (×50) of thenickel powder according to Example 1 of the present invention.

FIG. 2 This illustrates an optical microscope photograph (×100) of thenickel powder according to Example 2 of the present invention.

FIG. 3 This illustrates an SEM photograph (×1000) of the nickel powderaccording to Example 3 of the present invention.

FIG. 4 This illustrates an SEM photograph (×500) of the nickel powderaccording to Example 4 of the present invention.

FIG. 5 This illustrates an optical microscope photograph 5A (×50) and 5Bits enlarged photograph (×100) of the nickel powder according to Example4 of the present invention.

DETAILED DESCRIPTION

The present invention is a method for producing nickel powder including:producing nickel powder through a reduction treatment with hydrogen gasblown into a reactor as a pressurized container while adding seedcrystals to a nickel ammine sulfate complex solution and continuouslyfeeding the seed crystals; and continuously discharging the nickelpowder from the pressurized container. Moreover, a high purity, uniformfine nickel powder having lower sulfur grade can be obtained by using adispersant.

Hereinafter, the method for producing nickel powder according to thepresent invention will be described.

A nickel ammine sulfate complex solution that can be used in the presentinvention is not particularly limited, but it is suitable to use anickel ammine sulfate complex solution obtained by dissolving anickel-containing material, such as an industrial intermediate includingone or a mixture of two or more selected from nickel and cobalt mixedsulfide, crude nickel sulfate, nickel oxide, nickel hydroxide, nickelcarbonate, and nickel powder, with sulfuric acid or ammonia to prepare anickel-containing leachate (solution containing nickel), subjecting thenickel-containing leachate to a liquid-purification step such as solventextraction, ion exchange, or neutralization to remove impurity elementsin the solution, and adding ammonia to the resulting solution.

In the present invention, seed crystals are added to the nickel amminesulfate complex solution to form a slurry, which is subjected to thereduction treatment.

The seed crystals added here are powder having an average particle sizeof preferably 0.1 μm or more and 100 μm or less, more preferably 0.1 μmor more and 10 μm or less.

Nickel powder is suitably used as a substance which does not becomeimpurities in the final nickel precipitate to contaminate theprecipitate. The nickel powder used as the seed crystals can be preparedthrough addition of a reducing agent such as hydrazine to the nickelammine sulfate complex solution, for example.

The weight of the seed crystals to be added is preferably 1% by weightor more and 100% by weight or less based on the weight of the nickel inthe nickel ammine sulfate complex solution. A content of less than 1% byweight cannot sufficiently achieve the effect of reducing unevenprecipitation. A content of more than 100% by weight has no influencesover the effect; rather, it results in excess addition of the seedcrystals.

A dispersant may also be then added to disperse the seed crystals in theslurry.

Any polyacrylate dispersant can be used without particular limitation.Suitable is sodium polyacrylate because it is industrially available atlow cost.

If the dispersant is added, the amount thereof to be added is suitablyin the range of 0.5 to 5% by weight based on the weight of the seedcrystals. A content of less than 0.5% does not achieve any dispersingeffect. A content of more than 5% has no influences over the dispersingeffect; rather, such an addition is excess addition of the dispersant.

Alternatively, the polyacrylic acid may be added such that theconcentration thereof is 0.5 to 1.0 g/liter based on the amount of thenickel ammine sulfate complex solution. The seed crystals added at thistime are preferably seed crystals having an average particle size of 0.1μm or more and 10 μm or less.

In the present invention, for example, “to” in the description of 0.5 to5% by weight indicates 0.5% by weight or more and 5% by weight or less.

In the next step, the slurry prepared by adding the seed crystals or theseed crystals and the dispersant in the nickel ammine sulfate complexsolution is continuously placed into a reaction vessel of a containerresistant to high pressure and high temperature where a slurrycontaining ammonium sulfate and nickel powder is stored and the innerpressure is controlled with hydrogen gas. Thereby, a liquid phaseportion occupied by the slurry and a gaseous phase portion are formedwithin the reaction vessel. Alternatively, the slurry containing theseed crystals or the slurry containing the seed crystals and thedispersant, and the nickel ammine sulfate complex solution arecontinuously charged into a reaction vessel of a container resistant tohigh pressure and high temperature where a slurry containing ammoniumsulfate and nickel powder is stored and the inner pressure is controlledwith hydrogen gas. Thereby, a slurry is formed, and a liquid phaseportion occupied by the slurry and a gaseous phase portion having aninner pressure controlled with hydrogen gas is formed within thereaction vessel.

Subsequently, in the slurry continuously charged into the reactionvessel, the nickel complex ion contained in the nickel ammine sulfatecomplex solution is reduced with hydrogen gas to precipitate nickel onthe seed crystals added and grow the nickel precipitate into nickelpowder. The nickel powder slurry, i.e., the slurry containing the grownnickel powder is simultaneously formed, ant is continuously discharged.

The reaction temperature at this time is preferably in the range of 150°C. or more and 185° C. or less. A reaction temperature of less than 150°C. reduces the reduction efficiency. A reaction temperature of more than185° C. has no influences over the reaction; rather, it is not suitablebecause it increases loss of thermal energy.

Furthermore, the gaseous phase portion of the reaction vessel preferablyis under a pressure maintained in the range of 2.5 to 3.5 MPa during thereaction. A pressure of less than 2.5 MPa reduces the reactionefficiency. A pressure of more than 3.5 MPa has no influences over thereaction; rather, it increases loss of hydrogen gas.

A reduction treatment accompanied by the precipitation of nickel undersuch conditions can form a nickel precipitate on seed crystals and thusa grown nickel powder, continuously yielding nickel powder having alittle variation in size.

Moreover, because of the effect of the dispersant, nickel having lowersulfur grade can be extracted and recovered from the solution in theform of a fine powdery precipitate. In addition, a coarse nickel powderhaving a spherical shape and a smooth surface can also be yieldeddepending on the combination of the particle size of the nickel powderand the concentration of the dispersant.

The nickel powder produced as described above can be used inapplications of nickel pastes as an inner constitutional substance ofstacked ceramic capacitors. Besides, particles can be grown throughrepetition of the reduction with hydrogen to produce fine nickel metalwith high purity and uniformity which has a particle size of 20 μm orless and is suitable for handling.

EXAMPLES

Hereinafter, the present invention will be described by way of Examples.

Example 1

A pressurized container (autoclave) having an inner volume of 190 literwas used as a reaction vessel. A solution slurry (90 liter) containingammonium sulfate (269 g/L) and nickel powder (100 g/L) was placed intothe reaction vessel. The reaction vessel was covered with a lid tomaintain the temperature at 185° C. Hydrogen gas was then blown into thereaction vessel to control the pressure to 3.5 MPa.

In the next step, the starting solution containing 150 g/liter ofammonium sulfate and a nickel ammine sulfate complex solution(concentration of nickel: 110 g/L) was added to the pressurizedcontainer at a flow rate of 1 liter per minute, and further a nickelseed crystal slurry (concentration of slurry: 300 g/L) was added at aflow rate of 0.25 liter per minute to advance a reduction treatment.

The nickel powder used here as the seed crystals forming the nickel seedcrystal slurry had an average particle size of 1 μm. Hydrogen gas wasblown into the reaction vessel such that the inner pressure of thepressurized container was maintained at 3.5 MPa.

The following operation was continued for four hours: while the amountof the solution stored in the pressurized container was being controlledin the range of 90 liter±5 liter, the nickel powder slurry containingthe nickel powder produced in the reduction treatment was continuouslyextracted from the pressurized container. The reaction time in thereduction treatment in the reactor was 75 minutes from the charge of thestarting solution and the seed crystal slurry to the extraction of thenickel powder slurry.

As shown in Table 1-1, the extracted nickel powder slurry contained 0.28g/L of nickel, and the reduction rate (reaction rate), namely, theproportion of hydrogen gas used in the precipitation reaction of thenickel powder was 99.6%.

As shown in Table 1-2, particles having a particle size of 100 μm to 300μm were 99% or more of the particle diameter distribution, indicatingthat a sufficiently grown nickel powder was obtained.

In the entire particle diameter distribution, the proportion ofparticles having a particle size of more than 300 μm was less than 0.1%,the proportion of particles having a particle size of more than 150 μmand 300 μm or less was 91%, the proportion of particles having aparticle diameter of more than 100 μm and 150 μm or less was 8.3%, theproportion of particles having a particle diameter of more than 75 μmand 100 μm or less and the proportion of particles having a particlediameter of more than 45 μm and 75 μm or less both were less than 0.1%,and the proportion of particles having a particle diameter of 45 μm orless was 0.7%.

As shown in FIG. 1, although the particles having uneven shapes andaggregation are observed, it was confirmed that nickel powder having alittle variation in particle size distribution can be continuouslyproduced. The sulfur grade was 0.062%.

TABLE 1-1 Reaction time 4 [Hours] Concentration of Ni in Ni powderslurry 0.28 [g/L] Reduction rate 99.6 [%] S grade 0.062 [%]

TABLE 1-2 Reaction time 4 [Hours] Particle size [μm] Particle sizedistribution [%] 300 <0.1 300~+150 91 150~+100 8.3 100~+75  <0.1 75~+45<0.1 ~45 0.7

Example 2

The same reactor as in Example 1 was used. A solution slurry (90 liter)containing ammonium sulfate (205 g/L), polyacrylic acid (concentration:1 g/L), and nickel powder (concentration: 105 g/L) was placed into thereactor. The reaction vessel was covered with a lid to maintain theinner temperature at 185° C.

Hydrogen gas was then blown into the gaseous phase portion in thereactor to control the inner pressure of the container to 3.5 MPa.

In the next step, a starting solution containing a nickel ammine sulfatecomplex solution (concentration of nickel: 83 g/L) and ammonium sulfateat a concentration of 120 g/L was fed into the reactor at a flow rate of1 liter per minute, and simultaneously the nickel seed crystal slurry(concentration of slurry: 150 g/L) was continuously fed into the reactorat a flow rate of 0.5 liter per minute to advance the reductiontreatment.

Nickel powder having an average particle size of 1 μm was used as thenickel powder forming the nickel seed crystal slurry. Hydrogen gas wasblown such that the inner pressure of the reactor was maintained at 3.5MPa.

While controlling the amount of solution stored in the reactor to be inthe range of 90 liter±5 liter, the slurry subjected to the reductiontreatment was continuously extracted. This operation was continued forhours. The extracted slurry subjected to the reduction treatment wassubjected to solid liquid separation using a Nutsche funnel into nickelpowder and filtrate. The resulting nickel powder was washed, and wasvacuum dried. The reaction time in the reduction treatment in thereactor was 60 minutes from the charge of the starting solution and theseed crystal slurry to the extraction of the nickel powder slurry.

The reduction rate (reaction rate), namely, the proportion of hydrogengas used in the precipitation reaction of the nickel powder was 98.9%.

The resulting nickel powder had a finer average particle size D50 of 5.2μm but had a less variation in size than those of Example 1 (see FIG.2). Furthermore, the sulfur grade was 0.003%, which indicates that ahigh purity nickel powder having a low sulfur grade lower than thesulfur quality (0.01%) specified as the LME grade was obtained.

TABLE 2 Reaction time 16 [Hours] Reduction rate 98.9 [%] Particle size(D50) 5.2 [μm] S grade 0.003 [%]

Example 3

A solution (90 liter) containing ammonium sulfate (205 g/L), nickelpowder (105 g/L), and polyacrylic acid (1 g/L) was placed into a reactorhaving the same structure as in Example 1 and having a volume of 90liter to maintain the temperature at 185° C. Hydrogen gas was blown intothe reaction vessel to control the pressure at 3.5 MPa.

In the next step, a starting solution containing a nickel ammine sulfatecomplex solution (concentration of nickel: 83 g/L) and ammonium sulfateat a concentration of 120 g/L was added to this pressurized container ata rate of 1 liter/min, and simultaneously a nickel seed crystal slurry(slurry content: 150 g/L) was added at a rate of 0.5 liter/min.Moreover, polyacrylic acid at a concentration of 1 g/L was added to thenickel ammine sulfate complex solution in the starting solution, whichwas fed to the reactor. Hydrogen gas was blown into the pressurizedcontainer such that its pressure became 3.5 MPa. The extracted nickelpowder forming the nickel powder slurry had an average particle size of5.9 μm.

While the amount of the solution in the pressurized container was beingmanaged in the range of liter±5 liter, the nickel powder slurry wascontinuously extracted. This operation was continued for 12 hours. Thereaction time in the reduction treatment in the reactor was 60 minutesfrom the charge of the starting solution and the seed crystal slurry tothe extraction of the nickel powder slurry.

At this time, the reduction rate or the reaction rate was 96.8%.

The sulfur grade was 0.003%, which was lower than the sulfur grade(0.01%) specified as the LME grade.

The nickel powder had a particle size D50 of 6.4 μm, which indicatesthat a very fine powder could be stably obtained as shown in FIG. 3.

TABLE 3 Reaction time 12 [Hours] Reduction rate 96.8 [%] Particle size(D50) 6.4 [μm] S grade 0.003 [%]

Example 4

A starting solution (90 liter) containing ammonium sulfate (200 g/L),nickel powder (11 g/L), and polyacrylic acid (0.1 g/L) was placed intothe 90 liter reactor the same as that in Example 1 to maintain thetemperature at 185° C. Hydrogen gas was blown thereinto to control thepressure at 3.5 MPa.

A starting solution having a composition containing a nickel amminesulfate complex solution (concentration of nickel: 83 g/L) and 360 g/Lof ammonium sulfate was added to the reactor at a flow rate of 1liter/min, and a nickel seed crystal slurry (concentration: 33 g/L) wasadded at a rate of 0.5 liter/min. Hydrogen gas was blown into thepressurized container such that its pressure was maintained at 3.5 MPa,to advance the reduction treatment.

While the amount of the solution stored in the reactor was being managedin the range of 90 liter±5 liter, the nickel powder slurry subjected tothe reduction treatment was continuously extracted from the reactor.This operation was continued for 6 hours. The nickel powder forming the33 g/L nickel seed crystal slurry had an average particle size of 53 μm.The reaction time in the reduction treatment in the reactor was 60minutes from the charge of the starting solution and the seed crystalslurry to the extraction of the nickel powder slurry.

The reduction rate or the reaction rate was 89.0%.

The recovered nickel powder has a sulfur grade of 0.01%, which satisfiedthe sulfur grade (0.01%) specified as the LME grade.

The nickel powder had a particle size D50 of 78.0 μm, which indicatesthat a sufficiently grown nickel powder was obtained. As shown in FIGS.4 and 5, the nickel powder was obtained in the form of particles havingvery smooth surfaces and having a true spherical shape.

TABLE 4 Reaction time 6 [Hours] Reduction rate 89.0 [%] Particle size(D50) 78.0 [μm] S grade 0.01 [%]

Example 5

A pressurized container (autoclave) having an inner volume of 190 literand having inner walls lined with titanium was used as a reactor(reaction vessel). A solution slurry (90 liter) containing 205 g/literof ammonium sulfate, 1 g/liter of polyacrylic acid, and 105 g/liter ofnickel powder was placed into this reactor. The reactor was covered witha lid to maintain the temperature at 185° C.

Hydrogen gas was then blown into the gaseous phase portion of thereactor to control the inner pressure of the container to 3.5 MPa. Inthe next step, a nickel ammine sulfate complex solution (concentrationof nickel: g/liter) and a solution containing 120 g/liter of ammoniumsulfate were fed into this reactor at a flow rate of 1 liter per minute,and simultaneously 150 g/liter of nickel powder slurry was continuouslyfed into the reactor at a flow rate of 0.5 liter per minute.

Nickel powder having an average particle size of 1 μm was used forforming the nickel powder slurry. Hydrogen gas was blown into thereactor such that the inner pressure was maintained at 3.5 MPa.

In the next step, while the amount of the solution in the reactor wasbeing controlled in the range of 90 liter±5 liter, the nickel powderslurry was continuously extracted. This operation was continued forhours. The extracted nickel powder slurry was subjected to solid liquidseparation using a Nutsche funnel into nickel powder and a filtrate. Theresulting nickel powder was washed, and was vacuum dried.

The reduction rate (reaction rate), namely, the proportion of hydrogengas used in the precipitation reaction of the nickel powder was 98.9%.

The resulting nickel powder had an average particle size D50 of 5.2 μm.A fine nickel powder could be stably obtained.

Comparative Example 1

A solution having the same composition as in Example 1 was continuouslyfed, at the same flow rate, into the same reactor as in Example 1without containing polyacrylic acid, and was reduced with hydrogen gasunder the same condition as that in Example 1 to obtain a nickel powderslurry. The nickel powder slurry was subjected to solid liquidseparation to obtain nickel powder. The reduction rate or the reactionrate was 99.6%.

In the particle size distribution of the resulting nickel powder, theproportion of particles having a particle size of 100 μm to 300 μm was99% or more. In the entire particle size distribution, the proportion ofparticles having a particle size of more than 300 μm was less than 0.1%,the proportion of particles having a particle size of more than 150 μmand 300 μm or less was 91%, the proportion of particles having aparticle size of more than 100 μm and 150 μm or less was 8.3%, theproportion of particles having a particle size of more than 75 μm and100 μm or less and the proportion of particles having a particle size ofmore than 45 μm and μm or less both were less than 0.1%, and theproportion of particles having a particle size of 45 μm or less was0.7%. The resulting nickel powder was not fine as the nickel powderaccording to the present invention.

As described above, it was confirmed that a fine nickel powder can becontinuously and efficiently obtained by use of the method according tothe present invention.

1. A method of producing nickel powder, comprising feeding a nickelammine sulfate complex solution and seed crystals into a reactor, andfeeding hydrogen gas into the reactor to subject a nickel complex ion inthe nickel ammine sulfate complex solution to a reduction treatment andto thereby produce nickel powder having a sulfur grade of lower than0.01% by weight, wherein in the reduction treatment, while the nickelammine sulfate complex solution containing polyacrylic acid in aconcentration of 0.5 to 1.0 g/liter is being continuously fed into thereactor, a temperature inside the reactor is controlled within a rangeof 150 to 185° C. and a feed rate of hydrogen gas is controlled tomaintain an inner pressure of the reactor in a range of 2.5 to 3.5 MPato produce a nickel powder slurry containing the nickel powder, andthereafter, when the nickel powder slurry is extracted from the reactor,a feed amount of the nickel ammine sulfate complex solution and the seedcrystals and a discharge amount of the nickel powder slurry are adjustedto keep a given amount of the solution in the reactor.
 2. A method ofproducing nickel powder, comprising feeding hydrogen gas into a reactor,and feeding a nickel ammine sulfate complex solution and seed crystalsinto the reactor to subject a nickel complex ion in the nickel amminesulfate complex solution to a reduction treatment and to thereby producenickel powder having a sulfur grade of lower than 0.01% by weight,wherein in the reduction treatment, the nickel complex ion in the nickelammine sulfate complex solution is reduced in such a manner that aslurry containing ammonium sulfate and nickel powder are stored in thereactor to form a liquid phase portion and a gaseous phase portion inthe reactor and an inner pressure of the gaseous phase portion iscontrolled through the feeding of the hydrogen gas into the reactor, aslurry containing seed crystals and the nickel ammine sulfate complexsolution containing polyacrylic acid in a concentration of 0.5 to 1.0g/liter are continuously fed into the liquid phase portion, atemperature inside the reactor is controlled in a range of 150 to 185°C., and a feed rate of the hydrogen gas is controlled to maintain aninner pressure of the reactor in a range of 2.5 to 3.5 MPa to produce anickel powder slurry containing the nickel powder, and thereafter, whenthe nickel powder slurry is extracted from the reactor, a feed amount ofthe nickel ammine sulfate complex solution and the seed crystals and adischarge amount of the nickel powder slurry are adjusted to keep agiven amount of the solution in the reactor.
 3. (canceled)
 4. The methodof producing nickel powder according to claim 2, wherein nickel powderhaving an average particle size in a range of 0.1 to 100 μm is used asthe seed crystals.
 5. The method of producing nickel powder according toclaim 2, wherein nickel powder having an average particle size in arange of 0.1 to 10 μm is used as the seed crystals.
 6. The method ofproducing nickel powder according to claim 5, wherein an amount of theseed crystals to be added is in a range of 1 to 100% by weight based ona weight of nickel contained in the nickel ammine sulfate complexsolution.
 7. The method of producing nickel powder according to claim 6,wherein the nickel ammine sulfate complex solution subjected to thereduction treatment contains polyacrylic acid in an amount in a range of0.5 to 5% by weight based on a weight of the seed crystals in the nickelammine sulfate complex solution.
 8. The method of producing nickelpowder according to claim 7, wherein in the reduction treatment, thenickel ammine sulfate complex solution containing the seed crystals iscontinuously fed into the reactor such that a reaction time of thereduction treatment in the reactor takes 5 to 120 minutes.
 9. The methodof producing nickel powder according to claim 1, wherein nickel powderhaving an average particle size in a range of 0.1 to 100 μm is used asthe seed crystals.
 10. The method of producing nickel powder accordingto claim 1, wherein nickel powder having an average particle size in arange of 0.1 to 10 μm is used as the seed crystals.
 11. The method ofproducing nickel powder according to claim 1, wherein an amount of theseed crystals to be added is in a range of 1 to 100% by weight based ona weight of nickel contained in the nickel ammine sulfate complexsolution.
 12. The method of producing nickel powder according to claim1, wherein the nickel ammine sulfate complex solution subjected to thereduction treatment contains polyacrylic acid in an amount in a range of0.5 to 5% by weight based on a weight of the seed crystals in the nickelammine sulfate complex solution.
 13. The method of producing nickelpowder according to claim 1, wherein in the reduction treatment, thenickel ammine sulfate complex solution containing the seed crystals iscontinuously fed into the reactor such that a reaction time of thereduction treatment in the reactor takes 5 to 120 minutes.